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Crack Repair In Concrete Slab

Mike_Mills | Posted in General Discussion on January 15, 2010 04:25am

BACKGROUND – I have a hairline crack in my concrete patio slab. When it rains, it wicks moisture from outdoors in beneath the door sill, dampening the indoor portion of the slab. It does not get wet but does darken and get damp. If I want to put down flooring over the slab, this moisture is sure to be a problem. Wood flooring will soak it up like a sponge. So will carpeting. QUESTION – How do I repair this to stop the infiltration? MY GUESS – What do you think about this method? Ever tried it? Will it work? I was going to drill a 1/4″ to 1/2″ diameter hole down into the crack, all the way throught the slab, and fill with epoxy. I was going to then use my angle grinder to cut a groove that widens the top of the crack. I would back-fill the groove with more epoxy. Simpson Strong-Tie epoxy comes in caulk-gun tubes. It is grey with a sand filler and has a self-mixing, dispenser nozzle (super easy to use).

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  1. DanH | Jan 15, 2010 08:47pm | #1

    Probably as good as anything. Of course, it might be wise to put some sort of non-absorbent underlayment under the flooring, especially given that leaks under the door sill are still a possibility. (I'm guessing the sill isn't panned, or you likely wouldn't have this problem.)

    1. Mike_Mills | Jan 15, 2010 09:57pm | #2

      Thanks for the words of encouragment.

      The aluminum door threshold is on top of an inch of uncracked cementaceous self-leveling underlayment (SLU). The crack is in the concrete slab beneath the underlayment. The crack does not yield up a puddle or flow of water, it just gets damp. The crack wicks moisture beneath the underlayment.

      If there were an absorbent material (wood or carpet) in contact with the crack, I'm sure the absorber would take up a lot of moisture over time.

      If I were doing it again, I would just remove the old slab and pour a new, better-designed one (thicker and better reinforced). Live and learn.

  2. dovetail97128 | Jan 16, 2010 03:42am | #3

    Check out the Sika line of products.

    I would use a polyurethane crack or expansion joint filler/sealer, it will stay flexible.

    1. User avater
      Jeff_Clarke | Jan 16, 2010 07:58am | #4

      I second the Sika recommendation.

  3. User avater
    popawheelie | Jan 16, 2010 12:36pm | #5

    The silka crack filler is really thin and would penetrate into the crack.

    How about instead of drilling all the way through, just drill half way through.

    Then use a good caulking gun and cut the tube so it seals well in the hole you drilled.

    Wrap the caulking tube with duct tape to reinforce the tube.

    Only drill a few holes at first to see if the caulking will meet inbetween the two holes next to eachother. You should see the caulking come up out of the crack all the way between the two holes.

    To keep the caulking from coming up out of the carck to much tape on top but leave a gap in the middle of the two holes.

    I'd use a vaccum to clean the holes real well.

    Have plenty of solvent for clean up.

    I think you could pressure inject the Silka. It is really watery. Jaming the tube end in the hole and taping on top of the crack could keep the mess down to a minimum.

    Just an idea. Would a solvent in the crack prior to this help move the Silka? Your tape wouldn't stick with solvent on top of the concrete. Pour it down the hole?

    It depends on how wide the crack is.

    1. rbgator | Jan 16, 2010 07:52pm | #6

      You should determine the cause and extent of the moisture problem especially since it is infiltrating into your house. Is it runoff, groundwater, broken water line, etc.? You have more investigation options since your slab is outdoors and will be covered with flooring. The most conservative approach would be to cut back the slab about 12" from the house, find & correct the problem then backfill with well-graded sand & gravel, and install new slab with 8x8" thicken edge, and #5 dowels (8") @24"oc. I came upon your post by accident (now a new member). You can downgrade this solution to suit your time & $$$.

  4. User avater
    popawheelie | Jan 16, 2010 08:04pm | #7

    How about using Cyanoacrylate or crazy glue?

    The thin stuff is supposed to wick right into cracks.

    1. DanH | Jan 16, 2010 10:58pm | #8

      Crazy glue is too hard -- it has no "give".

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